In recent years, an organic EL device has attracted attention as a light-emitting device that can emit light with high luminance through low-voltage DC drive.
However, the organic EL device has a problem in that emission properties (e.g., luminance, luminous efficiency, and luminous uniformity) easily deteriorate with the passage of time.
It is considered that a deterioration in emission properties occurs when oxygen, water, and the like enter the organic EL device, and cause the electrode and the organic layer to deteriorate. Methods that utilize a sealing material have been proposed in order to solve this problem.
For example, Patent Document 1 discloses an organic EL device having a configuration in which a photocurable resin layer (sealing material) having humidity resistance covers an organic EL layer that is provided on a glass substrate and placed between a transparent electrode and a bottom electrode that are formed in the shape of a thin film. Patent Document 2 discloses a method that seals an organic EL device using a sealing film that is formed using a moisture-proof polymer film and an adhesive layer.
An acrylic-based adhesive and an acrylic-based pressure-sensitive adhesive (hereinafter referred to as “acrylic-based adhesive and the like”) have been proposed as an adhesive and a pressure-sensitive adhesive that are used as the sealing material for the organic EL device, taking account of optical properties such as transparency.
For example, Patent Document 3 discloses a UV-curable acrylic-based adhesive that can be cured at room temperature as a sealing material for an organic EL display.
Patent Document 4 discloses an acrylic-based pressure-sensitive adhesive as a pressure-sensitive adhesive that can form a pressure-sensitive adhesive layer that allows light emitted from an organic EL display device to propagate to the surface of the display with an excellent propagation efficiency even after being heated.
However, a sealing material that is formed using the acrylic-based adhesive and the like has an insufficient water barrier capability, and is not satisfactory as to performance when used as a sealing material for which a very high water barrier capability is required (e.g., the sealing material for the organic EL device).
When a sealing material that is formed using the acrylic-based adhesive and the like has a crosslinked structure, the sealing material may be easily delaminated from the adherend due to an impact, vibrations, heat, or the like, and the water barrier capability may deteriorate to a large extent.
In recent years, an adhesive that includes a polyisobutylene-based resin has been proposed as a sealing adhesive that exhibits a good water barrier capability.
For example, Patent Document 5 discloses an adhesive composition that is used as a sealing material for an organic EL display, and includes a specific hydrogenated cycloolefin-based polymer and a polyisobutylene resin.